This invention relates to interferometers, e.g., displacement measuring and dispersion interferometers that measure angular and linear displacements of a measurement object such as a mask stage or wafer stage in a lithography scanner or stepper system.
Displacement measuring interferometers monitor changes in the position of a measurement object relative to a reference object based on an optical interference signal. The interferometer generates the optical interference signal by overlapping and interfering a measurement beam reflected from the measurement object with a reference beam reflected from the reference object.
In many applications, the measurement and reference beams have orthogonal polarizations and different frequencies. The different frequencies can be produced, for example, by laser Zeeman splitting, by acousto-optical modulation, or internal to the laser using birefringent elements or the like. The orthogonal polarizations allow a polarizing beam splitter to direct the measurement and reference beams to the measurement and reference objects, respectively, and combine the reflected measurement and reference beams to form overlapping exit measurement and reference beams. The overlapping exit beams form an output beam that subsequently passes through a polarizer.
The polarizer mixes polarizations of the exit measurement and reference beams to form a mixed beam. Components of the exit measurement and reference beams in the mixed beam interfere with one another so that the intensity of the mixed beam varies with the relative phase of the exit measurement and reference beams. A detector measures the time-dependent intensity of the mixed beam and generates an electrical interference signal proportional to that intensity. Because the measurement and reference beams have different frequencies, the electrical interference signal includes a xe2x80x9cheterodynexe2x80x9d signal having a beat frequency equal to the difference between the frequencies of the exit measurement and reference beams. If the lengths of the measurement and reference paths are changing relative to one another, e.g., by translating a stage that includes the measurement object, the measured beat frequency includes a Doppler shift equal to 2 vnp/xcex, where v is the relative speed of the measurement and reference objects, xcex is the wavelength of the measurement and reference beams, n is the refractive index of the medium through which the light beams travel, e.g., air or vacuum, and p is the number of passes to the reference and measurement objects. Changes in the relative position of the measurement object correspond to changes in the phase of the measured interference signal, with a 2xcfx80 phase change substantially equal to a distance change L of xcex/(np), where L is a round-trip distance change, e.g., the change in distance to and from a stage that includes the measurement object.
Unfortunately, this equality is not always exact. In addition, the amplitude of the measured interference signal may be variable. A variable amplitude may subsequently reduce the accuracy of measured phase changes. Many interferometers include non-linearities such as what are known as xe2x80x9ccyclic errors.xe2x80x9d The cyclic errors can be expressed as contributions to the phase and/or the intensity of the measured interference signal and have a sinusoidal dependence on the change in optical path length pnL. In particular, the first harmonic cyclic error in phase has a sinusoidal dependence on (2 xcfx80pnL)/xcex and the second harmonic cyclic error in phase has a sinusoidal dependence on 2 (2 xcfx80pnL)/xcex. Higher harmonic cyclic errors can also be present.
There are also xe2x80x9cnon-cyclic non-linearitiesxe2x80x9d such as those caused by a change in lateral displacement (i.e., xe2x80x9cbeam shearxe2x80x9d) between the reference and measurement beam components of an output beam of an interferometer when the wavefronts of the reference and measurement beam components have wavefront errors. This can be explained as follows.
Inhomogeneities in the interferometer optics may cause wavefront errors in the reference and measurement beams. When the reference and measurement beams propagate collinearly with one another through such inhomogeneities, the resulting wavefront errors are identical and their contributions to the interferometric signal cancel each other out. More typically, however, the reference and measurement beam components of the output beam are laterally displaced from one another, i.e., they have a relative beam shear. Such beam shear causes the wavefront errors to contribute an error to the interferometric signal derived from the output beam.
Moreover, in many interferometry systems beam shear changes as the position or angular orientation of the measurement object changes. For example, a change in relative beam shear can be introduced by a change in the angular orientation of a plane mirror measurement object. Accordingly, a change in the angular orientation of the measurement object produces a corresponding error in the interferometric signal.
The effect of the beam shear and wavefront errors will depend upon procedures used to mix components of the output beam with respect to component polarization states and to detect the mixed output beam to generate an electrical interference signal. The mixed output beam may for example be detected by a detector without any focusing of the mixed beam onto the detector, by detecting the mixed output beam as a beam focused onto a detector, or by launching the mixed output beam into a single mode or multi-mode optical fiber and detecting a portion of the mixed output beam that is transmitted by the optical fiber. The effect of the beam shear and wavefront errors will also depend on properties of a beam stop should a beam stop be used in the procedure to detect the mixed output beam. Generally, the errors in the interferometric signal are compounded when an optical fiber is used to transmit the mixed output beam to the detector.
Amplitude variability of the measured interference signal can be the net result of a number of mechanisms. One mechanism is a relative beam shear of the reference and measurement components of the output beam that is for example a consequence of a change in orientation of the measurement object.
In dispersion measuring applications, optical path length measurements are made at multiple wavelengths, e.g., 532 nm and 1064 nm, and are used to measure dispersion of a gas in the measurement path of the distance measuring interferometer. The dispersion measurement can be used in converting the optical path length measured by a distance measuring interferometer into a physical length. Such a conversion can be important since changes in the measured optical path length can be caused by gas turbulence and/or by a change in the average density of the gas in the measurement arm even though the physical distance to the measurement object is unchanged.
The interferometers described above are often crucial components of scanner systems and stepper systems used in lithography to produce integrated circuits on semiconductor wafers. Such lithography systems typically include a translatable stage to support and fix the wafer, focusing optics used to direct a radiation beam onto the wafer, a scanner or stepper system for translating the stage relative to the exposure beam, and one or more interferometers. Each interferometer directs a measurement beam to, and receives a reflected measurement beam from, a plane mirror attached to the stage. Each interferometer interferes its reflected measurement beams with a corresponding reference beam, and collectively the interferometers accurately measure changes in the position of the stage relative to the radiation beam. The interferometers enable the lithography system to precisely control which regions of the wafer are exposed to the radiation beam.
In many lithography systems and other applications, the measurement object includes one or more plane mirrors to reflect the measurement beam from each interferometer. Small changes in the angular orientation of the measurement object, e.g., pitch and yaw of a stage, can alter the direction of each measurement beam reflected from the plane mirrors. If left uncompensated, the altered measurement beams reduce the overlap of the exit measurement and reference beams in each corresponding interferometer. Furthermore, these exit measurement and reference beams will not be propagating parallel to one another nor will their wave fronts be aligned when forming the mixed beam. As a result, the interference between the exit measurement and reference beams will vary across the transverse profile of the mixed beam, thereby corrupting the interference information encoded in the optical intensity measured by the detector.
To address this problem, many conventional interferometers include a retroreflector that redirects the measurement beam back to the plane mirror so that the measurement beam xe2x80x9cdouble passesxe2x80x9d the path between the interferometer and the measurement object. The presence of the retroreflector insures that the direction of the exit measurement is insensitive to changes in the angular orientation of the measurement object. However, even with the retroreflector, the lateral position of the exit measurement beam remains sensitive to changes in the angular orientation of the measurement object. Furthermore, the path of the measurement beam through optics within the interferometer also remains sensitive to changes in the angular orientation of the measurement object.
In practice, the interferometry systems are used to measure the position of the wafer stage along multiple measurement axes. For example, defining a Cartesian coordinate system in which the wafer stage lies in the x-y plane, measurements are typically made of the x and y positions of the stage as well as the angular orientation of the stage with respect to the z axis, as the wafer stage is translated along the x-y plane. Furthermore, it may be desirable to also monitor tilts of the wafer stage out of the x-y plane. For example, accurate characterization of such tilts may be necessary to calculate Abbe offset errors in the x and y positions. Thus, depending on the desired application, there may be up to five degrees of freedom to be measured. Moreover, in some applications, it is desirable to also monitor the position of the stage with respect to the z-axis, resulting in a sixth degree of freedom.
To measure each degree of freedom, an interferometer is used to monitor distance changes along a corresponding metrology axis. For example, in systems that measure the x and y positions of the stage as well as the angular orientation of the stage with respect to the x, y, and z axes, at least three spatially separated measurement beams reflect from one side of the wafer stage and at least two spatially separated measurement beams reflect from another side of the wafer stage. See, e.g., U.S. Pat. No. 5,801,832 entitled xe2x80x9cMethod of and Device for Repetitively Imaging a Mask Pattern on a Substrate Using Five Measuring Axes,xe2x80x9d the contents of which are incorporated herein by reference. Each measurement beam is recombined with a reference beam to monitor optical path length changes along the corresponding metrology axes. Because the different measurement beams contact the wafer stage at different locations, the angular orientation of the wafer stage can then be derived from appropriate combinations of the optical path length measurements. Accordingly, for each degree of freedom to be monitored, the system includes at least one measurement beam that contacts the wafer stage. Furthermore, as described above, each measurement beam may double-pass the wafer stage to prevent changes in the angular orientation of the wafer stage from corrupting the interferometric signal. The measurement beams may generated from physically separate interferometers or from multi-axes interferometers that generate multiple measurement beams.
The invention features multiple-degrees of freedom measuring interferometer assemblies and methods for measuring two, three and/or more degrees of freedom using a single interferometer optical assembly. For example, a two-degrees of freedom measuring plane mirror interferometer assembly may be configured to measure both a linear displacement and an angular displacement or two orthogonal angular displacements of a plane mirror. Furthermore, a three-degrees of freedom measuring plane mirror interferometer assembly may be configured to measure a linear displacement and two orthogonal angular displacements of a plane mirror or to measure two linear displacements and one angular displacement. Moreover, four or more degrees of freedom measuring plane mirror interferometer assembly may be configured to measure other combinations of linear and angular displacements.
In many embodiments, the interferometer directs a first set of two xe2x80x9cangle-measuringxe2x80x9d beams derived from a common input beam to contact a measurement object (e.g., a plane mirror measurement object) at two different locations and then combines the angle-measuring beams to produce a corresponding angle-measuring output beam. Because of optical differencing between the two angle-measuring beams, the angle-measuring output beam includes information about the changes in the angular orientation of the measurement object. Furthermore, in many embodiments, each of the angle-measuring beams contacts the measurement object only once, which tends to reduce sources of cyclic error non-linearities in the output signal.
The interferometer further directs one or more additional sets of beams along respective paths to produce one or more additional output beams that include information changes in the position or orientation of the measurement object with respect to additional degree(s) of freedom. For example, the interferometer may include a high stability plane mirror interferometer (HSPMI) portion for measuring changes in distance to the measurement object.
Embodiments of the interferometer may further include configurations that reduce or even eliminate differential beam shear between components of the angle-measuring output beam(s) at a detector or optical fiber pickup for coupling beams to the detector.
To measure multiple degrees of freedom, embodiments of the interferometer separate an input beam (or a progenitor input beam) into multiple sets of beams. In a first set of embodiments, the interferometer separates the progenitor input beam into two or more subsequent input beams (e.g., an angle-measuring input beam and a distance-measuring input beam) prior to any contact with the measurement object. In another set of embodiments, the interferometer separates an intermediate beam into multiple beams corresponding to the different degrees of freedom, where the intermediate beam includes a component (e.g., a xe2x80x9cprimaryxe2x80x9d measurement beam) that contacts the measurement beam at least once. In such embodiments, two or more of the output beams include a component that contacts the measurement object along a common path (e.g., the path defined by the primary measurement beam). Furthermore, in yet another set of embodiments, the interferometer separates a part of an output beam (e.g., an angle-measuring output beam) to define an additional input beam which is redirected back into the interferometer to measure an additional degree of freedom.
Typically, the interferometer assemblies are configured so that the beams that correspond to the different components in the output beams have optical path lengths of equal lengths in glass and/or equal lengths in a gas.
We now summarize different aspects and features of the invention.
In general, in one aspect, the invention features an apparatus including a multi-axis interferometer for measuring changes in a position of a measurement object (e.g., a plane mirror). The interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam. Each angle-measuring beam makes only a single pass to the measurement object before being combined to form the angle-measuring output beam. The interferometer is further configured to direct another set of beams derived from the progenitor input beam along different paths and then combine them to produce another output beam including information about changes in the position of the measurement object.
Embodiments of the apparatus may include any of the following features.
The other set of beams may include a first distance-measuring beam and a second distance-measuring beam and the other output beam may be a distance-measuring output beam. In such embodiments, the interferometer directs the first distance-measuring beam to make first and second passes to the measurement object and then combines it with the second distance-measuring beam to produce the distance-measuring output beam.
The interferometer may include a non-polarizing beam-splitter positioned to receive the progenitor input beam and separate it into an angle-measuring input beam and a distance-measuring input beam, wherein the first and second angle-measuring beams are derived from the angle-measuring input beam and the first and second distance-measuring beams are derived from the distance-measuring input beam. For example, the interferometer may include an angle-measuring optical assembly configured to direct the angle-measuring beams to the measurement object and a distance-measuring optical assembly configured to direct the distance measuring beams, wherein the angle-measuring optical assembly and distance-measuring optical assembly each include separate polarizing beam-splitters. The distance-measuring optical assembly may be configured as a high-stability plane mirror interferometer (HSPMI).
The interferometer may be configured to overlap the first angle-measuring beam with the first distance-measuring beam during their first pass to the measurement object. For example, the interferometer may include a non-polarizing beam-splitter positioned to separate the first angle-measuring beam from the first distance-measuring beam after their first pass to the measurement object.
The interferometer may include a non-polarizing beam-splitter positioned to receive the angle-measuring output beam and separate a portion of it to define a distance-measuring input beam, wherein the distance-measuring beams are derived from the distance-measuring input beam. Furthermore, in such embodiments, the interferometer may further include output fold optics positioned to direct the distance-measuring input beam, where the output fold optics include an a focal system having a magnification selected to cause the first distance-measuring beam to contact the measurement object at substantially normal incidence for a range of angular orientations of the measurement object. For example, the magnification may be 2:1.
The interferometer may be further configured to direct the first angle-measuring beam to make a pass to a reflective reference object after making the pass to the measurement object and before being combined with the second angle-measuring beam, and direct the second angle-measuring beam to make a pass to the reference object before making the pass to the measurement object. Moreover, the interferometer may be further configured to direct the second distance-measuring beam to make first and second passes to the reference object (e.g., a plane mirror).
The interferometer may include: a polarizing beam-splitter positioned to transmit one of each of the angle-measuring beams and the distance-measuring beams and reflect the other of each of the angle-measuring beams and the distance-measuring beams during each of the passes to the measurement and reference objects, and further positioned to recombine the angle-measuring beams to form the angle-measuring output beam and recombine the distance-measuring beams to form the distance-measuring output beam after the first and second passes; and a return optical assembly positioned to receive the angle-measuring and distance-measuring beams from the polarizing beam-splitter and redirect them back to the polarizing beam splitter between the first and second passes. The interferometer may include the reference object, or the reference object may be part of another measurement object such as in a differential plane mirror interferometer (DPMI). The interferometer may further includes a quarter-wave retarder positioned between the polarizing beam-splitter and the reference object and a quarter-wave retarder positioned between the polarizing beam-splitter and the measurement object.
The return optical assembly may include a half-wave retarder positioned to rotate the polarizations of the angle-measuring beams between the first and second passes. It may further includes an odd number of reflective surfaces positioned for the redirecting of the angle-measuring beams back to the polarizing beam-splitter. The odd number of reflective surfaces may each include a normal in a common plane. Moreover, the odd number of reflective surfaces may reflect the angle-measuring beams such that a sum of angles between incident and reflected beams at each of the reflective surfaces is zero or an integer multiple of 360 degrees, each angle measured in a direction from the incident beam to the reflected beam and having a positive value when measured in a counter clockwise direction and a negative value when measured in a clockwise direction. The return beam assembly may further include a retroreflector positioned for the redirecting of the distance-measuring beams back to the polarizing beam-splitter.
More generally, the return optical assembly may include a set of reflective surfaces positioned for the redirecting of the angle-measuring beams back to the polarizing beam-splitter, wherein the set of reflective surfaces reflect the angle-measuring beams such that a sum of angles between incident and reflected beams at each of the reflective surfaces is zero or an integer multiple of 360 degrees, each angle measured in a direction from the incident beam to the reflected beam and having a positive value when measured in a counter clockwise direction and a negative value when measured in a clockwise direction.
The interferometer may further include a non-polarizing beam-splitter positioned to receive the progenitor input beam and separate it into an angle-measuring input beam and a distance-measuring input beam, and wherein the polarizing beam-splitter is positioned to separate the angle-measuring input beam into the first and second angle-measuring beams and separate the distance-measuring input beam into the first and second distance-measuring beams.
The interferometer may be configured to direct the first angle-measuring beam to overlap with the first distance-measuring beam during their first pass to the measurement object and direct the second angle-measuring beam to overlap with the second distance-measuring beam during their first pass to the reference object. For example, the polarizing beam-splitter may be positioned to separate the progenitor input beam into a pair of overlapping beams including the first angle-measuring beam and the first distance-measuring beam and a pair of overlapping beams including the second angle-measuring beam and the second distance-measuring beam, and wherein the polarizing beam-splitter is further positioned to recombine the pairs of beams after their respective first passes to the measurement and reference objects to define an intermediate beam. Moreover, the return optical assembly may be positioned to receive the intermediate beam and include a non-polarizing beam-splitter positioned to separate spatially the angle-measuring beams from the distance-measuring beams.
The interferometer may include output fold optics including a non-polarizing beam-splitter positioned to receive the angle-measuring output beam and separate a portion of it to define a distance-measuring input beam, wherein the output fold optics are configured to direct the distance-measuring input beam to the polarizing beam-splitter, and wherein the polarizing beam-splitter is positioned to separate the distance-measuring input beam into the distance-measuring beams. Furthermore, the output fold optics may include an afocal system having a magnification selected to cause the first distance-measuring beam to contact the measurement object at substantially normal incidence for a range of angular orientations of the measurement object. For example, the magnification may be 2:1.
The apparatus may further include a light source configured to produce the progenitor input beam and direct it into the multi-axis interferometer, the progenitor input beam including two components having an heterodyne frequency splitting, wherein one of each of the angle-measuring beams and the other set of beams is derived from one of the components in the input beam, and the other of each of the angle-measuring beams and the other set of beams is derived from the other of the components in the input beam. For example, the components of the input beam may have orthogonal polarizations.
The apparatus may further include detectors configured to receive the output beams and generate electrical signals indicative of the changes in the angular orientation of, and the distance to, the measurement object. The apparatus may further include a polarization analyzer positioned prior to each detector and configured to pass an intermediate polarization to those of the components in each of the output beams. Furthermore, the apparatus may further include a fiber optic pick-up for coupling each output beam to a corresponding detector after it passes through the corresponding polarization analyzer.
The interferometer may further include an optical delay line positioned to reduce differential beam shear in the angle-measuring output beam. For example, the optical delay line may be positioned to introduce additional path length to the second angle-measuring beam during its return from the measurement object. In another example, the optical delay line may be configured to introduce a difference in path length between orthogonally polarized components of an incident beam. Moreover, the optical delay line may be positioned to receive the progenitor input beam and both of the output beams. In another example, the optical delay line may be positioned to receive the progenitor input beam and the distance-measuring output beam and the interferometer may include a second optical delay line positioned to receive the second the angle-measuring beam during its pass to the measurement object.
The interferometer may further include an optical delay block positioned to introduce additional path length to the second angle-measuring beam during its return from the measurement object to reduce differential beam shear in the angle-measuring output beam.
The first-mentioned angle-measuring output beam may include information about the angular orientation of the measurement object with respect to a first rotation axis. The interferometer may be further configured to direct a third angle-measuring beam derived from the progenitor input beam to make a pass to the measurement object, direct a fourth angle-measuring beam derived from the progenitor input beam to make a pass to the measurement object, and then combine the third and fourth angle-measuring beams to produce a second angle-measuring output beam including information about the angular orientation of the measurement object with respect to a second rotation axis different from the first rotation axis. For example, the second rotation axis may be orthogonal to the first rotation axis. The interferometer may be further configured to overlap the first and third angle-measuring beams during their pass to the measurement object.
In another aspect, the invention features a first apparatus including a multi-axis interferometer for measuring changes in an angular orientation of, and distance to, a measurement object. The interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam. The interferometer is further configured to direct another set of beams derived from the progenitor input beam along different paths and then combine them to produce another output beam including information about changes in the position of the measurement object. The interferometer includes a non-polarizing beam-splitter positioned to receive the progenitor input beam and separate it into an angle-measuring input beam and another input beam, wherein the first and second angle-measuring beams are derived from the angle-measuring input beam and the other set of beams are derived from the other input beam.
Embodiments of the second apparatus may further include features described above in connection with the first-mentioned apparatus.
In general, in another aspect, the invention features a third apparatus including a multi-axis interferometer for measuring changes in a position of a measurement object. The interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam. The interferometer is further configured to direct another set of beams derived from the progenitor input beam along different paths and then combine them to produce another output beam including information about changes in the position of the measurement object. During operation the first angle-measuring beam overlaps with a first one of the other set of beams during its first pass to the measurement object.
Embodiments of the third apparatus may further include features described above in connection with the first-mentioned apparatus.
In general, in another aspect, the invention features a fourth apparatus including a multi-axis interferometer for measuring changes in a position of a measurement object. The interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam. The interferometer is further configured to direct a first distance-measuring beam derived from the progenitor input beam to make first and second passes to the measurement object and then combine the first distance-measuring beam with a second-distance measuring beam derived from the progenitor input beam to produce a distance-measuring output beam. The interferometer includes a non-polarizing beam-splitter positioned to receive the angle-measuring output beam and separate a portion of it to define a distance-measuring input beam, wherein the distance-measuring beams are derived from the distance-measuring input beam. In some embodiments, the interferometer further includes fold optics positioned to direct the distance-measuring input beam, the fold optics including an afocal system having a magnification selected to cause the first distance-measuring beam portion to contact the measurement object at substantially normal incidence for a range of angular orientations of the measurement object.
Embodiments of the fourth apparatus may further include features described above in connection with the first-mentioned apparatus.
In general, in another aspect, the invention features a fifth apparatus including a multi-axis interferometer for measuring changes in a position of a measurement object. The interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam. The interferometer is further configured to direct another set of beams derived from the progenitor input beam along different paths and then combine them to produce another output beam including information about changes in the position of the measurement object. The interferometer includes a polarizing beam-splitter positioned to combine the first angle-measuring beam with the second angle-measuring beam after the first angle-measuring beam makes its pass to the measurement object but before the second angle-measuring beam makes its pass to the measurement object, the combined beams defining an intermediate beam. The interferometer further includes a return optical assembly positioned to receive the intermediate beam and direct it back to the polarizing beam-splitter, the return optical assembly includes a set of reflective surfaces positioned to reflect the intermediate beam an odd number of times in a plane defined by the incidence of the angle-measuring beams on the measurement object, and wherein the return optical assembly further include a half-wave plate configured rotate the polarization of each angle-measuring beam in the intermediate beam.
Embodiments of the fifth apparatus may further include features described above in connection with the first-mentioned apparatus.
In general, in another aspect, the invention features a method including: directing a first angle-measuring changes in a position of a measurement object; directing a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object; combining the angle-measuring beams after their passes to the measurement object to produce an angle-measuring output beam; directing another set of beams derived from the progenitor input beam along different paths; and combining the other set of beams to produce another output beam including information about changes in the position of the measurement object. In preferred embodiments, wherein each angle-measuring beam makes only a single pass to the measurement object.
The method may further include additional features corresponding to any of the features described above in connection with the different apparatus.
In another aspect, the invention features a lithography system for use in fabricating integrated circuits on a wafer. The lithography system includes: a stage for supporting the wafer; an illumination system for imaging spatially patterned radiation onto the wafer; a positioning system for adjusting the position of the stage relative to the imaged radiation; and any of the interferometric apparatus described above for monitoring the position of the wafer relative to the imaged radiation.
In another aspect, the invention features another lithography system for use in fabricating integrated circuits on a wafer. This lithography system includes: a stage for supporting the wafer; and an illumination system including a radiation source, a mask, a positioning system, a lens assembly, and any of the interferometric apparatus described above. During operation the source directs radiation through the mask to produce spatially patterned radiation, the positioning system adjusts the position of the mask relative to the radiation from the source, the lens assembly images the spatially patterned radiation onto the wafer, and the interferometry system monitors the position of the mask relative to the radiation from the source.
In another aspect, the invention features a beam writing system for use in fabricating a lithography mask. The beam writing system includes: a source providing a write beam to pattern a substrate; a stage supporting the substrate; a beam directing assembly for delivering the write beam to the substrate; a positioning system for positioning the stage and beam directing assembly relative one another; and any of the interferometric apparatus described above for monitoring the position of the stage relative to the beam directing assembly.
In another aspect, the invention features a lithography method for use in fabricating integrated circuits on a wafer. The lithography method includes: supporting the wafer on a moveable stage; imaging spatially patterned radiation onto the wafer; adjusting the position of the stage; and monitoring the position of the stage using any of the interferometric methods described above.
In another aspect, the invention features another lithography method for use in the fabrication of integrated circuits. This lithography method includes: directing input radiation through a mask to produce spatially patterned radiation; positioning the mask relative to the input radiation; monitoring the position of the mask relative to the input radiation using any of the interferometry methods described above; and imaging the spatially patterned radiation onto a wafer.
In another aspect, the invention features a third lithography method for fabricating integrated circuits on a wafer including: positioning a first component of a lithography system relative to a second component of a lithography system to expose the wafer to spatially patterned radiation; and monitoring the position of the first component relative to the second component using any of the interferometric methods described above.
In another aspect, the invention features a method for fabricating integrated circuits, the method including any of the lithography methods described above.
In another aspect, the invention features a method for fabricating integrated circuits, the method including using any of the lithography systems described above.
In another aspect, the invention features a method for fabricating a lithography mask, the method including: directing a write beam to a substrate to pattern the substrate; positioning the substrate relative to the write beam; and monitoring the position of the substrate relative to the write beam using any of the interferometry methods described above.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict with publications, patent applications, patents, and other references mentioned incorporated herein by reference, the present specification, including definitions, will control.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.